1. Field of the Present Invention
The present invention generally relates to methods and apparatus for thermal management in electronic equipment enclosures, and, in particular, to the effects of perforations in various walls and other panels of enclosures on temperature, air flow and other thermal phenomena.
2. Background
Racks, frames and enclosures for mounting and storing computer and other electronic components or equipment (hereinafter referred to as “electronic equipment”) have been well known for many years. Racks and frames are typically simple rectangular frameworks on which electronic equipment may be mounted, or on which other mounting members, such as shelves or brackets, may be mounted which in turn may support the electronic equipment. Enclosures are typically frames on which panels or doors, or both, are hung to provide aesthetic improvement, to protect the equipment from external influences, to provide security for the equipment stored inside, or for other reasons.
Racks, frames and enclosures have been built in many different sizes and with many different proportions in order to best accommodate the equipment which they are designed to store. Electronic equipment stored in these enclosures may include audio and video equipment and the like, but quite frequently include computer equipment and related peripheral devices. These components typically include housings enclosing internal operative elements.
The electronic equipment housed in the enclosures generate large amounts of thermal energy. The enclosures frequently make use of fans and perforated panels, among other things, to help control the thermal energy and maximize the flow of cooling air through the enclosure and exhausting heated air therefrom. Such panels are perhaps most frequently used on doors, but may also be used in top, bottom, side, front and back walls and in interior surfaces as well, such as shelves or partitions.
The supply of cool air to the enclosure, and the transfer of thermal energy from the electronic equipment, is conventionally handled by a Computer Room Air Conditioner (“CRAC”). Airflow into the enclosure generally relies solely or at least primarily on the air pressure differential as measured between the entry point of air into the room and the ambient room. However, active means are often used to push or pull heated air out of the enclosures.
For a particular component, thermal energy is transferred from its housing using forced air convection. More specifically, internal fans draw or push air through the housing from front-to-rear over the heated internal elements within the housing. The air absorbs the thermal energy from the internal elements and carries it away as it exits the housing.
Airflow through a particular component housing is primarily controlled by the internal fan installed by the manufacturer. While it is possible to reduce this throughput by constricting air flow through an enclosure, it is difficult to appreciably increase the airflow through a component housing.
One way in which enclosure manufacturers have tried to increase airflow to an enclosure is to increase the number of perforations in an enclosure panel. For a panel, the ratio of the openings created by perforations therein to the total area of the panel can be expressed as the “percent open area” (or “percent open”) of the panel. Equipment manufacturers have sometimes specified a minimum percent open for third party enclosures being used to house their equipment. Typically, equipment manufacturers have specified a minimum percent open of 63%. Enclosures are presently available that provide panels with percent open values ranging up to 80% open. If no panel whatsoever is used, the resulting opening may be described as 100% open.
Despite the presence of perforated panels and fans, the ability to run an efficient data center can be a challenge especially when dealing with legacy installations while trying to plan for future applications. The principles of data center design for effective thermal management with high density data communications equipment heat loads are frequently violated. More often than not these violations come via an acquisition of previously developed space or habitation of mature space designed for equipment with lower heat loads.
There are a number of standard practices and a few creative patches that are used in an attempt to minimize or neutralize the resultant hot spots caused by these violations. These patches include adding high static pressure blowers to the bottom spaces of equipment enclosures; plugging all sources of bypass air; creating barriers to hot air recirculation, such as internal enclosure air dams, enclosure top return air isolation panels, and closed duct return air paths; and adding floor fans to deliver more cold air to the fronts of enclosures.
Another approach that has commonly been used is the removal of one or more panels, such as a front door or another easily-removed panel, from the enclosure itself, thus resulting in a “100% open” opening. This has been traditionally thought to maximize the amount of air-flow through the opening, even when the panel thus removed already had at least some perforations therethrough, and in particular, even when the percent open area created by the perforations was already as great as the minimum specified by equipment manufacturers. It has further traditionally been thought that maximizing airflow through the enclosure maximized removal of thermal energy from the enclosure. Unfortunately, the removal of such a panel is not an ideal solution, since it results in a security risk, is inconvenient for the user, and causes other problems.
In addition, it has traditionally been thought that providing a maximum percent open in a perforated panel maximizes the amount of airflow through and thus thermal energy removed from the enclosure. However, as percent open increases, the thickness of the panel is typically reduced. As the thickness of the perforated panel decreases, so to does the security and stability of the enclosure. Therefore, increasing the percent open of a perforated panel is also not always an ideal solution. This issue becomes particularly critical as the percent open is increased beyond about 63%.
Thus, a need exists for a perforation solution that maximizes the relative benefit achieved by airflow through the enclosure while still maintaining the various advantages provided by relatively thick panels rather than thin panels or uncovered openings. More particularly, the effectiveness of removing panels from an equipment enclosure or using a relatively thin perforated panel with a percent open greater than 63% relative to the benefits provided by relatively thicker perforated panels with a percent open of 63% or less has not previously been understood in the enclosure industry. As a result, the design process for panels for electronic equipment enclosures has been inexact, and designers have been forced to vary multiple design parameters for a particular panel during their design process in an effort to develop a design that satisfies the various criteria for the panel.